Method for passively determining the application of a sample fluid on an analyte strip

Abstract

The present invention relates to a method for passively determining the application of a sample fluid on an analyte strip using measurement of ambient light passing through the strip. Sample fluid, such as whole blood, is applied to a reagent matrix and the amount of ambient light transmitted through the matrix is periodically measured both before and after application of the sample fluid. A step increase of the transmitted light reading occurs after hydration of the strip, and the occurrence of this step increase is used to start a predetermined incubation period. At the expiration of the incubation period, another light transmission measurement is made which is indicative of an analyte concentration in the sample fluid (such as glucose concentration in a whole blood sample).

What is claimed is: 
     
       1. A method for determining a start of reaction timing for measurement of a reaction between a sample fluid and a reagent, comprising the steps of: a) measuring a transmission of light through the reagent at intervals prior to application of the sample fluid to the reagent;   b) applying the sample fluid to the reagent;   c) measuring the transmission of light through the reagent/sample fluid combination at intervals after performing step (b);   d) determining a location of a step increase in the measurement data taken at steps (a) and (c);   e) beginning a predetermined time period at a time corresponding to the step increase; and   f) measuring the transmission of light through the reagent sample fluid combination after expiration of the predetermined time period.   
     
     
       2. The method of claim 1, wherein the sample fluid is whole blood. 
     
     
       3. The method of claim 2, wherein the reagent reacts with the whole blood to produce a color change in proportion to an amount of glucose in the whole blood. 
     
     
       4. The method of claim 1, wherein step (a) comprises measuring an amount of ambient light transmitted through the reagent. 
     
     
       5. The method of claim 1, wherein steps (c) and (f) comprise measuring an amount of ambient light transmitted through the reagent. 
     
     
       6. The method of claim 1, wherein the intervals are fixed intervals. 
     
     
       7. The method of claim 1, further comprising the steps of: g) determining a magnitude of the light transmission measured at step (a); and   h) adjusting an integration time of subsequent measurements based upon the magnitude determined at step (g).